Heretofore, as a covering material for agricultural greenhouses, a fluororesin film such as an ethylene/tetrafluoroethylene copolymer (ETFE) film, which is excellent in durability, transparency, strength, etc., has been used.
In recent years, the application of a fluororesin film expands to film structures other than the covering material for agricultural greenhouses, for example, a roof material of large-scale greenhouses and atria, an exterior wall and a roof material of sports facilities, etc., on the basis of its performance.
Such a film structure is employed mainly in Europe, Chine, etc. at the present stage, but in the other countries, it has not substantially been employed at present due to the difference in the fire protection standard. Particularly in Japan, a non-reinforced resin film has not been allowed as a building material by the Building Standards Law of Japan, since the film is burned out by 6 cm square fire as stipulated in the fire test.
Further, to build a large-scale film structure in Japan, a design considering the wind speed in the typhoon or the monsoon in winter is inevitable, but of the fluororesin film at present, the strength is insufficient. Accordingly, consideration is required such that the distance between supports of a panel which supports the film is shortened, the thickness of the film is increased, or several layers of films are overlaid, and accordingly the degree of freedom in the design and advantages in the building cost may not be made use of.
On the other hand, heretofore, a laminated sheet comprising a resin film laminated on cloth made of glass fibers (hereinafter referred to as glass fiber cloth) has been used in various fields.
As the glass fiber cloth, a woven or nonwoven fabric comprising glass fibers has been commonly used. Further, the woven or nonwoven fabric usually has a binder (paste) treatment applied so as to prevent slippage of the glass fibers. As the material for the binder, a solution or a dispersion of a melamine resin, an acrylic-melamine resin, an acrylic resin, an ethylene/vinyl acetate resin or the like is commercially available.
Further, particularly for building application, as the resin film, a fluororesin film which is excellent in weather resistance, stain resistance, water resistance, etc. is widely used.
For example, Patent Document 1 discloses an incombustible sheet comprising a fluororesin film melt-pasted on incombustible cloth such as a glass fiber cloth.
Further, Patent Document 2 discloses a waterproof cloth comprising a fluororesin film fused and bonded to a base cloth obtained by twisting composite yarn obtained by impregnating multifilament yarn comprising glass fibers having a diameter of 6 microns or smaller with a fluororesin such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride in a predetermined amount, followed by firing.
Patent Document 1: JP-A-61-61849
Patent Document 2: JP-B-5-3826